Depending on electric characteristics, nano tubes can be embodied into electric elements such as diodes and transistors. A carbon nano tube (CNT), for example, is a graphite hollow cylinder having a diameter on the order of several angstroms. Structurally, the CNT is similar to a hexagonal lattice of cylinder-type carbon. The CNT has a quantum characteristic at a low temperature, and the characteristics of a metal or a semiconductor, depending on its chirality.
The metal type CNT can carry a current of high density with a given resistance. The semiconductor type CNT can be switched on and off like a field effect transistor (FET). The two types of nano tubes can also be combined (sharing electrons). Due to these characteristics, the CNT is an optimum material for the fabrication of a nano-meter-sized semiconductor circuit. The CNT can be, for example, a one-dimensional electric conductor, which means that a one-dimensional quantum mechanical mode carries a current.
A CNT based transistor has advantageous electrical properties because diffusion in the material is inhibited, which can enhance device performance.
In the manufacturing of semiconductor devices, a gate of the current transistor generally includes gate forming materials such as tungsten (W), polysilicon, poly germanium silicide, and tungsten silicide. However, because these gate forming materials have a large resistance, the whole speed of the transistor is reduced and power consumption is increased. Additionally, when the size of the semiconductor is decreased by a conventional method, a resistance of a gate is increased. Thus, it is necessary to develop improved materials.
CNTs have been proposed as new gate forming materials to overcome the problems resulting from the scale-down of semiconductors. A method for forming a gate using a CNT, however, has not been commercialized.
In the conventional method for forming a CNT, the CNT has a cylinder structure, so that a contact surface with silicon (Si) becomes narrow. As a result, it is difficult to control subsequent processes after formation of the CNT gate. It is also necessary to prevent a short channel effect.